Fix default value for properties to match attributres.

PiperOrigin-RevId: 183001593

Author: alorenzen

_tests/test/compiler/ast_template_parser_test.dart

@@ -568,12 +568,13 @@ void main() {
               selector: '[a]',
               type: new CompileTypeMetadata(
                   moduleUrl: someModuleUrl, name: 'DirA'),
-              inputs: ['a']);
-          expect(humanizeTplAst(parse('<div a></div>', [dirA])), [
+              inputs: ['a', 'b']);
+          expect(humanizeTplAst(parse('<div a [b]></div>', [dirA])), [
             [ElementAst, 'div'],
             [AttrAst, 'a', ''],
             [DirectiveAst, dirA],
-            [BoundDirectivePropertyAst, 'a', '']
+            [BoundDirectivePropertyAst, 'a', ''],
+            [BoundDirectivePropertyAst, 'b', '']
           ]);
         });
 
@@ -1273,7 +1274,7 @@ void main() {
           expect(humanizeTplAst(parse('<div *ngIf></div>', [ngIf])), [
             [EmbeddedTemplateAst],
             [DirectiveAst, ngIf],
-            [BoundDirectivePropertyAst, 'ngIf', 'null'],
+            [BoundDirectivePropertyAst, 'ngIf', ''],
             [ElementAst, 'div']
           ]);
         });

_tests/test/compiler/template_parser_test.dart

@@ -516,12 +516,13 @@ void main() {
               selector: "[a]",
               type: new CompileTypeMetadata(
                   moduleUrl: someModuleUrl, name: "DirA"),
-              inputs: ["a"]);
-          expect(humanizeTplAst(parse("<div a></div>", [dirA])), [
+              inputs: ["a", "b"]);
+          expect(humanizeTplAst(parse("<div a [b]></div>", [dirA])), [
             [ElementAst, "div"],
             [AttrAst, "a", ""],
             [DirectiveAst, dirA],
-            [BoundDirectivePropertyAst, "a", ""]
+            [BoundDirectivePropertyAst, "a", ""],
+            [BoundDirectivePropertyAst, "b", ""],
           ]);
         });
 

angular/lib/src/compiler/ast_template_parser.dart

@@ -404,7 +404,7 @@ class _BindDirectivesVisitor
       [_ParseContext context]) {
     try {
       var value = context.templateContext.parser.parseBinding(
-          astNode.value ?? 'null',
+          astNode.value ?? '',
           _location(astNode),
           context.templateContext.exports);
       // If we bind the property to a directive input, or the element is a